High-pressure tank and method for fabricating the same

ABSTRACT

An annular fitting recess is formed circumferentially in the exterior of a tank body in the vicinity of the boundary between a dome section and a cylindrical gas discharge section of the tank body. A cylindrical reinforcing collar is fitted onto the cylindrical gas discharge section of the tank body to fit an annular boss of the reinforcing collar in the fitting recess of the tank body and then engaged integrally on the exterior of the tank body between the cylindrical gas discharge section and the dome section by shrinkage. This provides easily and inexpensively a high-pressure tank capable of withstanding high pressures of 35 to 75 MPa while keeping its lightness in weight.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to improvements of a high-pressure tank intowhich high-pressure gas is charged and improvements of a method forfabricating the same.

(2) Description of the Related Art

High-pressure tanks into which a gas, such as natural gas or hydrogengas, is charged and stored at high pressure, are generally subjected towinding which is a technique for wrapping carbon fibers or the likearound the tank body for reinforcement. A cylindrical gas dischargesection and a continuous dome section of the tank, in particular, arelikely to concentrate stress and therefore must be reinforced firmly.However, the vicinity of the boundary between the dome section and thecylindrical gas discharge section is difficult to subject to winding andthus difficult to reinforce.

Therefore, the dome section and the cylindrical gas discharge sectionare generally increased in thickness as compared with a cylindricalmiddle section of the tank by necking a predetermined region of anelongated hollow cylindrical blank continuing from its opening end bymeans of spinning.

In this connection, the applicant filed a patent application on atechnique for further thickening the dome section and the cylindricalgas discharge section by flow forming the predetermined region of theelongated hollow cylindrical blank continuing from its opening end intoa larger thickness than the other region and then necking the thickenedpredetermined region through spinning, and has already obtained a patentfor the technique (see, for example, patent document 1)

[Patent Document 1]

Japanese Patent Publication No. 3251216 (page 3 and FIG. 1)

For the first-mentioned technique, however, there is a limit to how muchthe thickness of the dome section and the cylindrical gas dischargesection can be increased because of the use of an elongated hollowcylindrical blank having a uniform thickness as a whole. Therefore, thistechnique is difficult to apply particularly to high-pressure tanks forhydrogen gas into which the gas is charged at a pressure of between 35MPa and 75 MPa.

To cope with this, it can be considered to ensure the thickness of thedome section and the cylindrical gas discharge section by increasing thethickness of the entire middle section of the elongated hollowcylindrical blank. In this case, however, the entire high-pressure tankthus fabricated will also be thickened and thereby increased in weight,which hinders weight reduction. In addition, since the tank uses thethick elongated hollow cylindrical blank, its material cost will behigh.

On the other hand, for the second-mentioned patent document 1, since thepredetermined region of the elongated hollow cylindrical blankcontinuing from the opening end is increased in thickness as comparedwith the other region, the dome section and the cylindrical gasdischarge section can have a larger thickness as compared with thefirst-mentioned technique and the entire tank weight can be reduced bythinning the middle section. This patent document 1 technique, however,requires the elongated hollow cylindrical blank to undergo two processsteps of flow forming and spinning, which takes much labor. In addition,in order to ensure a sufficient thickness of a dome section and acylindrical gas discharge section in a high-pressure tank for hydrogengas, it is necessary to increase the amount of reduction of the blank.This may invite the complete closure of the cylindrical gas dischargesection and thereby necessitate subsequent boring of a gas outlet in alater process step, which requires extra labor.

SUMMARY OF THE INVENTION

The present invention has been made in view of the foregoing points andtherefore its object is to provide easily and inexpensively ahigh-pressure tank capable of withstanding high pressures of 35 to 75MPa while keeping its lightness in weight.

To attain the above object, the present invention is characterized inthat a reinforcing member is fitted integrally on the exterior of thetank between the cylindrical gas discharge section and the dome section,and takes the following solutions.

The invention claimed in claims 1 to 3 is concerned with a high-pressuretank. The invention claimed in claim 1 is characterized by comprising: ametallic tank body in which a cylindrical gas discharge section isprotruded integrally from one end of a cylindrical middle sectionthrough a dome section and an annular fitting recess is formedcircumferentially in the exterior of the tank body in the vicinity ofthe boundary between the dome section and the cylindrical gas dischargesection; and a cylindrical metallic reinforcing collar having an annularboss and engaged integrally on the exterior of the tank body between thecylindrical gas discharge section and the dome section with the bossfitted in the fitting recess of the dome section through fitting of thereinforcing collar onto the cylindrical gas discharge section of thetank body.

With the above structure, in the invention of claim 1, the cylindricalgas discharge section and the neighboring dome section, likely toconcentrate stress, can be increased in effective thickness by thethickness of the reinforcing collar, thereby obtaining sufficientstrength in these sections. This provides a high-pressure tank strongenough to withstand high pressures of 35 to 75 MPa. Further, since thereinforcing collar is fitted not on the entire tank body but only on itspart: the dome section and the cylindrical gas discharge section, thisdoes not so much increase the weight of the entire high-pressure tankand maintains light weight, and provides facilitated fabrication andreduced cost.

The invention claimed in claim 2 is characterized in that in theinvention of claim 1, the reinforcing collar is made of steel alloy ortitanium alloy.

With the above structure, in the invention of claim 2, the dome sectionand the cylindrical gas discharge section, likely to concentrate stress,can be further increased in strength thanks to the mechanical propertiesof steel alloy or titanium alloy which is a material for the reinforcingcollar.

The invention claimed in claim 3 is characterized in that in theinvention of claim 1, the tank body is made of aluminum alloy.

With the above structure, in the invention of claim 3, the tank body ofaluminum alloy is light in weight, which further reduces the tank weightas a whole.

The invention claimed in claim 4 is concerned with a method forfabricating a high-pressure tank. The method is characterized bycomprising the steps of: plastically deforming a hollow cylindricalblank of metal with rotation to form a tank body in which a cylindricalgas discharge section is protruded integrally from one end of acylindrical middle section through a dome section, followed by formingan annular fitting recess circumferentially in the exterior of the tankbody in the vicinity of the boundary between the dome section and thecylindrical gas discharge section; and then fitting a cylindricalmetallic reinforcing collar having an annular boss onto the cylindricalgas discharge section of the tank body to fit the boss in the fittingrecess of the dome section and engaging the reinforcing collarintegrally on the exterior of the tank body between the cylindrical gasdischarge section and the dome section by shrinkage.

With the above structure, in the invention of claim 4, the additionalreinforcing collar need only be fitted onto the cylindrical gasdischarge section of the tank body. Accordingly, a high-pressure tankhaving a light weight and capable of withstanding high pressures of 35to 75 MPa can be fabricated easily without requiring much labor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional view of a high-pressure tank.

FIG. 2 is a longitudinal cross-sectional view of a reinforcing collar.

FIG. 3A is a longitudinal cross-sectional view of a short hollowcylindrical blank provided for flow forming in a high-pressure tankfabrication process.

FIG. 3B is a diagram showing a flow forming step in the high-pressuretank fabrication process.

FIG. 3C is a diagram showing a spinning step in the high-pressure tankfabrication process.

FIG. 3D is a longitudinal cross-sectional view showing a state that, adome section of a tank body is formed with a fitting recess in thehigh-pressure tank fabrication process.

FIG. 3E is a longitudinal cross-sectional view showing a state before areinforcing collar is fitted onto the tank body by shrinkage in thehigh-pressure tank fabrication process.

FIG. 3F is a longitudinal cross-sectional view showing a state that thereinforcing collar is fitted onto the tank body by shrinkage in thehigh-pressure tank fabrication process.

DESCRIPTION OF PREFERRED EMBODIMENT

Hereinafter, an embodiment of the present invention will be describedwith reference to the drawings.

FIG. 1 shows a high-pressure tank 1 according to the embodiment of thepresent invention. The high-pressure tank 1 includes a tank body 2 intowhich high-pressure gas, such as hydrogen gas, of 35 to 75 MPa ischarged. The tank body 2 is formed so that a cylindrical gas dischargesection 5 circular in cross section is protruded integrally from one endof a cylindrical middle section 3 circular in cross section through adome section 4, the cylindrical gas discharge section 4 is formed with agas outlet 6 and the cylindrical middle section 3 is integrally formedat the other end with a bottom section 7. The tank body 2 is providedinternally with a hollow part 8 for containing high-pressure gas.

The high-pressure tank 1 is made of aluminum alloy such as JIS A 6061 orJIS A 6062, formed by plastically deforming a hollow cylindrical blankand subjected to heat treatment such as T6 treatment after the forming.The dome section 4, the cylindrical gas discharge section 5 and thebottom section 7 are formed to have greater thicknesses than thecylindrical middle section 3. In particular, the dome section 4 is, dueto its forming process, gradually increased in thickness from that ofthe middle section 3 to that of the cylindrical gas discharge section 5in proceeding from the middle section 3 to the cylindrical gas dischargesection 5, thereby reinforcing the dome section 4 which is likely toconcentrate stress. Further, an annular fitting recess 9 is formedcircumferentially in the exterior of the tank body in the vicinity ofthe boundary between the dome section 4 and the cylindrical gasdischarge section 5.

As a feature of the present invention, a cylindrical metallicreinforcing collar 10 is engaged integrally onto the exterior of thetank body 2 between the cylindrical gas discharge section 5 and the domesection 4 by shrinkage. The reinforcing collar 10 is, as also shown inFIG. 2, composed of a cylindrical part 11 of circular cross sectionhaving substantially the same thickness as the cylindrical gas dischargesection 5, and an extension 12 formed integrally at the lower end of thecylindrical part 11 to extend outwardly. The extension 12 is graduallyreduced in thickness proceeding to its outer edge, so that the outeredge of the extension 12 merges with the exterior of the dome section 4smoothly. The back of the extension 12 is formed integrally with anannular boss 13 which protrudes downwardly. The reinforcing collar 10 isformed internally with a fitting hole 14 which passes through thecylindrical part 11 and the extension 12 vertically. The reinforcingcollar 10 is made of steel alloy, such as SNCM440, SCM440 or SKD61, ortitanium alloy and formed by forging or turning. Materials for thereinforcing collar, however, are not limited to the above but need onlybe those higher in strength-to-weight ratio than aluminum. Suchmaterials make a great contribution to weight reduction. Further, thecylindrical part 11 of the reinforcing collar 10 is fitted integrally onthe cylindrical gas discharge section 5 of the tank body 2 by shrinkagewith the cylindrical gas discharge section 5 inserted in the fittinghole 14, and the extension 12 of the reinforcing collar 10 is bondedintegrally to the exterior of the dome section 4 by shrinkage with theboss 13 fitted in the fitting recess 9 of the dome section 4.

As described above, the cylindrical gas discharge section 5 and theneighboring dome section 4 has a larger thickness as compared with thecylindrical middle section 3. The fitting of the reinforcing collar 10on these sections can further increase their effective thickness, and inaddition increase their strength much more in combination with themechanical properties of steel alloy or titanium alloy which is amaterial for the reinforcing collar 10. Accordingly, there can beprovided a high-pressure tank 1 strong enough to withstandhigh-pressures of 35 to 75 MPa.

Further, since the fitting position of the reinforcing collar 10 is notthe entire tank body 2 but limited to the dome section 4 and thecylindrical gas discharge section 5 which are likely to concentratestress, this avoids a large increase in weight of the high-pressure tank1, thereby keeping its lightness in weight, and provides facilitatedfabrication and reduced cost. Furthermore, since the tank body 2 is madeof aluminum alloy and therefore light in weight, the tank weight can befurther reduced as a whole.

Next, description will be made about an example of fabrication methodsfor the high-pressure tank 1 having the above-described structure.

First, prepared is a short hollow cylindrical blank 21 of aluminum alloyas shown in FIG. 3A. The short hollow cylindrical blank 21 is formed,for example, by forging a solid cylindrical billet, which is not shown,and has the shape of an end-closed cylinder in which a cylindricalmiddle section 31 is formed integrally with a bottom section 71.Alternatively, the shape of an end-closed cylinder may be formed bydrawing a disk-shaped material with a die and a punch.

Then, the short hollow cylindrical blank 21 is flow formed. The mannerof the flow forming is as shown in FIG. 3B: the short hollow cylindricalblank 21 is fitted on a mandrel 15, the mandrel 15 is rotated on itsaxis to rotate the short hollow cylindrical blank 21 as a single unit,and a forming roll 16 is pressed against the outer periphery of theshort hollow cylindrical blank 21 to rotate while applying force to themiddle section 31 in the axial direction. In this manner, the shorthollow cylindrical blank 21 is plastically deformed to form an elongatedhollow cylindrical blank 211. At this stage, the thicknesses of a middlesection 311 and a bottom section 711 become equal to those of a middlesection 3 and a bottom section 7 of a tank body 2 in a tank as a finalproduct.

Subsequently, the elongated hollow cylindrical blank 211 is held by anunshown chucking device, and a predetermined region starting from theopening end is necked by spinning. The manner of the necking in processis as shown in FIG. 3C: the elongated hollow cylindrical blank 211 isrotated on its axis, and in this state a forming roll 17 is pressed inan inclined position against the predetermined region starting from theopening end of the elongated hollow cylindrical blank 211 to rotatewhile moving obliquely with respect to the axis of the elongated hollowcylindrical blank 211. In this manner, the predetermined region startingfrom the opening end of the elongated hollow cylindrical blank 211 isplastically deformed, resulting in the formation of a tank body 2 inwhich a cylindrical gas discharge section 5 is protruded integrally fromone end of a cylindrical middle section 3 through a dome section 4. Thetank body 2 is formed so that the dome section 4 is gradually increasedin thickness proceeding from the cylindrical middle section 3 to thecylindrical gas discharge section 5 through the necking by spinning asdescribed above.

Then, the tank body 2 is loaded into a cutting machine, and as shown inFIG. 3D, an annular fitting recess 9 is formed circumferentially in theexterior of the tank body 2 in the vicinity of the boundary between thedome section 4 and the cylindrical gas discharge section 5.

Thereafter, as shown in FIG. 3E, prepared is a reinforcing collar 10 ofsteel alloy or titanium alloy obtained by an additional forging orturning. As described above, the reinforcing collar 10 has a cylindricalpart 11 and an extension 12 formed integrally at the lower end of thecylindrical part 11, the back of the extension 12 is formed integrallywith an annular boss 13, and the reinforcing collar 10 is formedinternally with a fitting hole 14 which passes through the cylindricalpart 11 and the extension 12 vertically (see FIG. 2). The inner diameterof the fitting hole 14 is selected by taking into consideration afitting allowance for shrinkage relative to the outer diameter of thecylindrical gas discharge section 5.

Then, as shown in FIG. 3F, the reinforcing collar 10 is fitted onto thecylindrical gas discharge section 5 of the tank body 2 so that the boss13 of the reinforcing collar 10 is fitted in the fitting recess 9 of thedome section 4. Subsequently, the reinforcing collar 10 is engagedintegrally on the exterior of the tank body 2 between the cylindricalgas discharge section 5 and the dome section 4 by shrinkage.

As can be understood from the above, the additionally preparedreinforcing collar 10 need only be fitted onto the cylindrical gasdischarge section 5 of the tank body 2. Accordingly, a high-pressuretank 1 can be fabricated easily without requiring much labor.

In the above embodiment, an end-closed cylindrical blank is illustratedas the short hollow cylindrical blank 21 provided for flow forming.However, the short hollow cylindrical blank 21 may be a hollow cylinderboth ends of which are open. In this case, predetermined regionsrespectively starting from both opening ends will be necked by spinning.

1. A high-pressure tank comprising: a metallic tank body in which anintegral cylindrical gas discharge section is protruded outwardly fromone end of a cylindrical middle section through a dome section and aannular fitting recess is formed circumferentially in the exterior ofthe tank body in the vicinity of the boundary between the dome sectionand the cylindrical gas discharge section; and a cylindrical metallicreinforcing collar having annular boss and engaged integrally on theexterior of the tank body between the cylindrical gas discharge sectionand the dome section with the boss fitted in the fitting recess of thedome section through fitting the reinforcing collar onto the cylindricalgas discharge section of the tank body, wherein a thickness of thecylindrical gas discharge section and an adjacent portion of the domesection is greater than a thickness of the cylindrical middle section.2. The high-pressure tank of claim 1, wherein the reinforcing collar ismade of steel alloy or titanium alloy.
 3. The high-pressure tank ofclaim 1, wherein the tank body is made of aluminum alloy.
 4. Thehigh-pressure tank as defined in claim 1, wherein the fitting of thereinforcing collar increases an effective thickness of the cylindricalgas discharge section and the adjacent portion of the dome section. 5.The high-pressure tank as defined in claim 4, wherein the reinforcingcollar is formed of at least one of a steel alloy and a titanium alloyfor increasing the strength of the cylindrical gas discharge section andthe dome section.
 6. The high-pressure tank as defined in claim 5,wherein the cylindrical gas discharge section and the dome section ofthe tank are formed of an aluminum alloy.
 7. The high-pressure tank asdefined in claim 1, wherein the high-pressure tank can contain ahigh-pressure gas at a pressure in a range of 35 to 75 MPa.
 8. Thehigh-pressure tank as defined in claim 1, wherein the high-pressure tankcan contain a high-pressure gas at a pressure in a range of 35 to 75MPa.
 9. The high-pressure tank as defined in claim 4, wherein thehigh-pressure tank can contain a high-pressure gas at a pressure in arange of 35 to 75 MPa.
 10. The high-pressure tank as defined in claim 5,wherein the high-pressure tank can contain a high-pressure gas at apressure in a range of 35 to 75 MPa.
 11. The high-pressure tank asdefined in claim 6, wherein the high-pressure tank can contain ahigh-pressure gas at a pressure in a range of 35 to 75 MPa.